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Environmental Science
Chapter 8 Understanding Populations
Name ________________________________
Date ______________ Period ______
Section 1: How Populations Change in Size
Read the passage below and answer the questions that follow.
Over time, the growth rates of populations change because birth rates and death rates increase or
decrease. Growth rates can be positive, negative, or zero. For a population’s growth rate to be
zero, the average number of births must equal the average number of deaths. A population would
remain the same size if each pair of adults produced exactly two offspring, and each of those
offspring survived to reproduce. If the adults in a population are not replaced by new births, the
growth rate will be negative and the population will shrink.
Write the letter of the term or phrase that best matches the description.
a. positive growth rate
b. negative growth rate
c. zero growth rate
_____ 1. The average number of deaths is greater than the average number of births.
_____ 2. The average number of deaths equals the average number of births.
_____ 3. The average number of births is greater than the average number of deaths.
4. Growth rate is the birth rate minus the ____________________________.
5. Suppose that each year, one half of a population has 2 offspring per person, and the other half
has none. If all members of the population die after a year, what is the resulting growth rate?
_______________ Explain your answer. _____________________________________________
______________________________________________________________________________
Sequence the statements below to illustrate zero population growth. Write “1” on the line in
front of the first step, “2” on the line in front of the second step, and so on.
______ 6. The population size returns to what it was in year x.
______ 7. Two adults produce two offspring in year x.
______ 8. The offspring, as adults, reproduce one offspring each.
______ 9. The parents die.
Read each question and write the answer in the space provided.
10. Explain the difference between negative growth rate and zero growth rate. _______________________
__________________________________________________________________________________
11. What is similar about negative growth rate and zero growth rate? ______________________________
__________________________________________________________________________________
12. What would be the result if a population did not replace its deaths with new births? _________________
__________________________________________________________________________________
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Section 2: How Species Interact with Each Other
Read the passage below and answer the questions that follow.
An organism that lives in or on another organism and feeds on the other organism is a parasite. The
organism the parasite takes its nourishment from is known as the host. The relationship between the
parasite and its host is called parasitism. Examples of parasites are ticks, fleas, tapeworms, heartworms,
bloodsucking leeches, and mistletoe.
Photos of parasites may make you feel uneasy, because parasites are somewhat like predators. The
differences between a parasite and a predator are that a parasite spends some of its life in or on the host,
and that a parasite does not usually kill its host. In fact, the parasite has an evolutionary advantage if it
allows its host to live longer. However, the host is often weakened by or exposed to disease from the
parasite.
Read each question and write the answer in the space provided.
1. Give four examples of parasites. _________________________________________________________
___________________________________________________________________________________
2. What does a parasite get from its host? ____________________________________________________
3. What is the relationship between a parasite and its host called? _________________________________
In the space provided, write the letter of the term or phrase that best completes each statement/question.
_____ 4. A parasite
a. takes nourishment from another organism.
b. always eventually kills its host.
_____ 5. A host
a. is like a predator.
b. is the organism a parasite lives on or in.
c. cannot live in mistletoe.
d. All of the above
c. may make you feel uneasy.
d. usually kills its parasite
6. The prefix para- means “alongside,” while the Greek word sitos means “grain” or “food.” Use this
information to define parasite. ___________________________________________________________
___________________________________________________________________________________
7. If the suffix -ism means “the practice of,” how would you define parasitism? _______________________
___________________________________________________________________________________
8. How are parasites and predators alike? ____________________________________________________
9. How are parasites and predators different? _________________________________________________
___________________________________________________________________________________
10. Why is it beneficial for a parasite to allow its host to live? _____________________________________
___________________________________________________________________________________
11. What effect does a parasite’s presence usually have on its host? _______________________________
___________________________________________________________________________________
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Concept Review
MATCHING Write the letter of the description that best matches the term or phrase
____1. interaction between two species in which both are harmed
a. density
b. growth rate
c. reproductive potential
d. carrying capacity
e. density independent
f. niche
g. habitat
h. competition
i. parasitism
j. coevolution
____ 2. the functional role of a species within an ecosystem
____ 3. one of the three main properties of a population
____ 4. development of adaptations as a result of symbiotic relationships
____ 5. maximum population that an ecosystem can support indefinitely
____ 6. close interaction between two species in which one organism
benefits while the other organism is harmed
____ 7. the ratio of births to deaths in a population
____ 8. maximum # of offspring that each member of a population can produce
____ 9. a reduction in population size caused by a natural disaster
____10. the location where an organism lives
MULTIPLE CHOICE Write the letter of the term/phrase that best completes each statement/question.
_____ 11. A territory is a place/area
a. where one animal lives. b. where people eat. c. defended by one or more individuals. d. for sleeping.
_____ 12. Which of the following is an example of a parasite?
a. worm in your intestine b. lion hunting zebras c. bee stinger in your arm
d. honeybee on a flower
____ 13. Bacteria in your intestines are an example of mutualism if they
a. make you sick.
b. have no effect.
c. are destroyed by digestive juices.
d. help break down food.
_____ 14. Predators ___ kill their prey.
a. always
b. usually
c. never
d. try not to
_____ 15. What property of a population may be described as even, clumped, or random?
a. dispersion
b. density
c. size
d. growth rate
_____ 16. What can occur if a population has plenty of food and space, and no competition or predators?
a. reduction of carrying capacity
b. exponential growth
c. zero population growth
d. coevolution
_____ 17. A grizzly bear can be all of the following except a
a. parasite.
b. competitor.
c. mutualist.
_____ 18. The “co-” in coevolution means
a. apart.
d. predator.
b. together.
c. two.
d. predator-prey.
_____ 19. Which of the following has the greatest effect on reproductive potential?
a. producing more offspring at a time
b. reproducing more often
c. having a longer life span
d. reproducing earlier in life
_____ 20. Members of a species may compete with one another for
a. running faster.
b. social dominance.
c. giving birth.
d. mutualism.
_____ 21. A robin that does not affect the tree in which it nests is an example of
a. parasitism.
b. commensalism.
c. mutualism.
d. predation.
_____ 22. Two species can be indirect competitors for food if they
a. use the same food source at different times.
c. fight over food.
b. have different food sources.
d. eat together peacefully.
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Read the following, and answer the questions below.
Imagine that two species of monkeys are introduced to an island that provides them with an ideal habitat.
One species is arboreal and eats fruits and leaves; the other is terrestrial and relies on fallen fruits and a
few small insects it can pick from the ground for survival. The monkeys have an abundance of food, no local
competition for the food, and no predators. After a decade, the number of frugivorous and leaf-eating
arboreal monkeys increased faster than the terrestrial fruit and insect eaters. After 20 years, the number of
terrestrial monkeys in the island started to decrease rapidly, although the arboreal monkey population
remained fairly stable.
23. Explain what probably caused the changes in the two monkey populations. _______________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
24. What type of biological interaction best explains the relative greater success of the arboreal monkeys?
___________________________________________________________________________________
___________________________________________________________________________________
25. Is the terrestrial population of monkeys destined to extinction? Explain __________________________
___________________________________________________________________________________
___________________________________________________________________________________
AGREE OR DISAGREE - Agree or disagree with the following statements; support your answers.
26. The only competitors that humans have for food are other humans and Insects. ___________________
__________________________________________________________________________________
__________________________________________________________________________________
27. The interaction generated by human intervention to protect the gray wolf population in the northwestern
United States can be defined as commensalism. ___________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
28. Although there are many predators on the African savanna, none plays exactly the same role as the
lion. Can any two species occupy exactly the same niche? Why or why not? ______________________
__________________________________________________________________________________
29. To be considered part of the same population organisms must have a reasonable chance of mating with
each other. Are two wild roses separated by a wide road part of the same population? Defend your
answer. ____________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
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